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Recording a 12-lead ECG

  • Procedure

Ten electrodes on the limbs and chest record the heart's electrical activity; exact positions and a still, relaxed patient give a tracing that can be trusted.

Updated

What it is

The 12-lead electrocardiogram records the heart's electrical activity from twelve views using ten electrodes: four on the limbs and six on the chest (V1 to V6). It is painless and sends no electricity into the body. Its value depends on technique: electrodes in the wrong place, oily or hairy skin, movement or shivering create false changes. The machine prints an automatic reading, but a qualified clinician must interpret the tracing, and an abnormal pattern in a patient with symptoms is an urgent finding.

Indications

  • Chest pain or symptoms that may be cardiac.
  • Palpitations, fainting or breathlessness.
  • Baseline before procedures or treatments that affect the heart.
  • Electrolyte disorders and follow-up of known rhythm problems.

Contraindications and precautions

  • There is no absolute contraindication; in an emergency the ECG must not delay care.
  • Ask about allergy to the electrode adhesive.
  • Note a pacemaker or implanted device on the request and the tracing.
  • Respect privacy: expose only what is needed and cover the patient afterwards.

Equipment

  • ECG machine with paper or digital storage, checked and charged.
  • Ten electrodes within their expiry date.
  • Gauze or cloth to clean and dry the skin, and clippers if there is hair.
  • Screen, sheet, clean gloves if needed and a pen.

Step by step (and why)

  1. Check the order, identify the patient, ask about allergies and explain it is painless — reduces anxiety and movement.
  2. Ensure privacy, lay the patient flat, expose the chest and enter the patient's data — the tracing stays identified.
  3. Remove oil, moisture and hair at each site and check the electrode expiry date — good contact reduces artefact.
  4. Place the four limb electrodes on the arms and legs as their labels show (RA, LA, RL, LL) — each has a fixed place.
  5. Place V1 and V2 in the 4th intercostal space at the right and left sternal borders, as the protocol shows — exact placement.
  6. Place V4 at the 5th space midclavicular, V3 between V2 and V4, then V5 and V6 level with V4 — standard views.
  7. Ask the patient to stay still and breathe normally, and record — movement and talking create artefact.
  8. Check quality and labels; repeat if there is artefact — a poor tracing can hide or simulate disease.
  9. Remove electrodes, clean and check the skin, and hand the tracing to the clinician promptly — speeds a decision.

Complications

  • Artefact from movement, shivering, poor contact or loose cables.
  • False changes from misplaced chest electrodes or swapped limb leads.
  • Skin irritation at the electrode sites.
  • Delayed treatment if an abnormal tracing is not shown to the clinician quickly.

Next step: when to call for help

  • If the tracing looks abnormal, check consciousness, pulse, chest pain and breathlessness, and call for emergency help if needed.
  • Report chest pain during the recording and hand over the ECG at once.
  • Give every ECG to the treating clinician promptly, even when the automatic reading says normal.

Test yourself

Think of the answer, then tap the question to see it.

Where are V1 and V2 placed?

In the 4th intercostal space: V1 at the right sternal border and V2 at the left sternal border.

Where is V4 placed, and how are V5 and V6 positioned?

V4 in the 5th intercostal space at the midclavicular line; V5 on the anterior axillary line and V6 on the midaxillary line, both level with V4.

Why must the patient lie still and warm during the recording?

Because movement and shivering add artefact that can hide or imitate real changes.

Can the nurse rely on the machine's automatic reading?

No. The tracing must be interpreted by a qualified clinician, and an abnormal pattern with symptoms is reported at once.

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Connections

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Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.

Sources: Nursing Advanced Skills, 7.7: Checklist - Obtain a 12-Lead ECG (Open RN (Chippewa Valley Technical College), LibreTexts, 2023); Electrocardiogram: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Nursing Advanced Skills, 7.2: Basic Concepts (Open RN (Chippewa Valley Technical College), LibreTexts, 2023).

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Representative model, for educational purposes only.